Molded-one piece articles are used, for example in forming printed circuit boards. In many instances, two separate molding steps are used to form two portions of the article. For example, two-shot molding is a means of producing devices having two portions, with each portion made from a different injection molded polymer. The process is also used for producing two-colored molded plastic articles and for combining hard and soft plastics in one molded part.
A typical two-shot molding process includes the following steps:                1. Mold first shot;        2. Overmold first shot with second polymer;        3. Etch and activate exposed areas; and        4. Plate with electroless nickel and/or electroless copper to deposit plating material.        
In addition to possessing the required end use properties for the product, the two polymers selected for use must be compatible in the two-shot molding process and must also provide suitable surfaces for plating. In order to plate one of the polymers and not the other, it has generally been found necessary to either selectively activate the polymer to be plated after the molding process or to use a polymer having a catalyst disposed therein, i.e., a polymer containing a certain percentage of palladium, as described for example in U.S. Pat. No. 7,189,120 to Zaderej, the subject matter of which is herein incorporated by reference in its entirety. Other examples of two-shot (or multi-shot) molding processes are described in U.S. Pat. No. 5,407,622 to Cleveland et al. and in U.S. Pat. No. 6,601,296 to Dailey et al., the subject matter of each of which is herein incorporated by reference in its entirety. Still other processes that have been suggested include (i) embedding a catalyst in all of the plastic and then selectively exposing it and activating it by means of selective laser ablation, (ii) the use of double-shot molding wherein one shot contains catalytic poisons to prevent plating in that area and, (iii) double shot (or multiple-shot) molding, wherein the plastic in the plateable shot is easily etched to form a surface conducive to catalyzation and plating and the unplateable shot is not easily etched.
Typical plastic materials that can be made conducive to catalyzation and plating include acrylonitrile-butadiene-styrene (ABS) resins, polyolefins, polyvinyl chloride, polycarbonate-acrylonitrile-butadiene-styrene (PC/ABS) resins, and phenol formaldehyde resins, among others.
The process for forming an electroless coating (plating on plastics cycle) typically involves the steps of (1) etching the substrate; (2) neutralizing the etched surface; (3) catalyzing the neutralized surface in a solution that contains palladium chloride, stannous chloride and hydrochloric acid, or an acidic solution of ionic palladium, followed by (4) immersion in an accelerator solution, which is either an acid or a base; and (4) forming a metallic coating on the activated substrate. The surface of the substrate is generally etched by dipping the substrate in an etchant, which is typically a mixed solution of chromic acid and sulfuric acid. The metallic coating may be deposited on the activated substrate by immersing the substrate in a chemical plating bath containing nickel or copper ions and depositing the metal thereon from the bath by means of the chemical reduction of the metallic ions (i.e., electroless plating). The resulting metal coating is useful for subsequent electroplating because of its electrical conductivity. It is also generally desirable to wash the substrate with water after each of the above steps.
This method has two major drawbacks:                (1) The conventional and lowest cost materials for this process are acrylonitrile-butadiene-styrene (ABS), polycarbonate-acrylonitrile-butadiene-styrene (PC/ABS) and polycarbonate (PC). Each of these materials are etched by blends of chromic and sulfuric acid to some extent leaving a narrow window of operation for getting full plating where desired and no plating where not desired at the same time; and        (2) Due to the inclusion of chromic acid, the etching solution is very objectionable from environmental, health and safety perspectives.        
Thus, it would be desirable to provide a means of selectively plating on plastics, including acrylonitrile-butadiene-styrene and acrylonitrile-butadiene styrene/polycarbonate resins that does not require the use of a chromic acid etchant.
Surface modification of polymers, such as sulfonation, has been used for improving polymer properties by changing the hydrophobic surfaces to hydrophilic surfaces. Sulfonation has been achieved using several methods including treatment with vapor phase sulfur trioxide, hot concentrated sulfuric acid, and fuming sulfuric acid, among others. Sulfonation alters the chemical structure of a polymeric substrate by introducing sulfonic groups on its surface region. The process of treating the surface region with sulfur trioxide gas and various neutralization agents to modify the molecular structure of the surface region of the plastic can be effective on a wide variety of polymers. Sulfonation has been suggested for use in activating the surface of a molded plastic article to accept a silane coating material thereon, as discussed for example in U.S. Pat. No. 5,958,509 to Neumann et al., the subject matter of which is herein incorporated by reference in its entirety
In the sulfonation process, SO3 bonds to the carbon atoms present in the polymers and forms C—SO3H. This a process generally described as the sulfur atom (S) bonding to the carbon atom (C) in the carbon backbone of the polymer. Essentially all commercially available plastics and films contain either a CH or an NH bond and are treatable via sulfonation, although the inventors of the present invention have found that sulfonation proceeds at different rates depending on the particular polymer resin being sulfonated. For NH containing materials, NSO3H, results as opposed to C—SO3H.
The present invention relates generally to the sulfonation of molded articles having a first portion that is receptive to electroless plating thereon and a second portion which substantially inhibits electroless plating thereon. More particularly, the present invention relates to processes for forming molded blanks for printed circuit boards and molded articles and plating portions of the articles which are made with two separate molding steps to form plateable and unplateable portions of the articles.